This invention relates to improvements in a railway coupler for withstanding repetitive stress loadings on parts thereof, and more particularly to an improved knuckle construction to avoid knuckle pin failure, particularly due to bending loads by supporting the pin within the knuckle in a manner that prevents bending moments that cause the knuckle pin to fail because of fatigue fracture.
In conventional railway couplers, coupling of cars is accomplished by means of interlocking knuckles which can be either in compression or tension, depending upon the direction of movement of a train. When movement of the train reverses, and the knuckles change from a tension condition to a compression condition, the nose of each knuckle tends to slam into the throat portion of the other. After a period of time, this results in a metal fatigue condition with attendant cracks in the throat region of the knuckle. Complex and repetitive stress loadings on the coupler, particularly the knuckle pin thereof, cause fatigue fracturing due to bending loads on the pin. The bending loads are imposed on the knuckle pin upon movement of a train from a stop condition as well as when the train reverses direction from a buff condition to a draft condition. Other conditions occur during the use of railway couplers that bring about repetitive stress loadings as either a static and/or dynamic loading on the knuckle pin. These conditions include movement of a train over vertical track level variations; a rocking and rolling of the car body; and rotation of a railway car for dumping while coupled to other cars by interlocking couplers constructed to accommodate rotary movement between the cars. These conditions exist irrespective of whether standard AAR F-type couplers or E-type couplers are used. Moreover, in an E-type coupler, the nose portion of one knuckle can slide vertically through a distance of about one-half the knuckle height of the mating coupler. As is well known in the art, an E-type coupler does not include interlocking lugs and aligning wing pockets which are predominant features of F-type coupler heads. In F-type couplers, the interlocking lugs prevent vertical sliding of one knuckle relative to a mating knuckle. Because of this interlocking feature of F-type coupler heads, they are usually selected to embody a construction to permit rotation of a car while coupled to another car. Failure of a knuckle pin due to fatigue fracture is not always detected when the fracture occurs because sometimes parts of the fractured pin remain in place; thus, permitting rotation of the knuckle on the coupler head. An unsafe condition does, however, exist because the fractured pin parts can fall from the coupler. Frequently, part of a fractured pin falls out of a coupler of a car when the car is rotated for dumping.
Fatigue failure of knuckle pins usually only occurs when the coupler and knuckle surfaces which are load bearing become worn or experience unusual service conditions. Sometimes, however, a knuckle pin in a new coupler can be stressed beyond the elastic limit of the material of the pin. The present invention is based on the surprising discovery that by supporting at least the midportion of the knuckle pin against bending in a direction transverse to the pin length will prevent pin failure, particularly due to fatigue fracture in all known couplers. Sometimes, in the past, knuckles of couplers were strengthened in the throat area by modification to a core used in a casting to produce upper and lower circular openings which are seperated by an intermediate cavity of larger cross-sectional area than the circular openings. The wall between the outer surface of the throat and the inner surface of the cavity had an increased thickness at the center of the pivot pin hole to reinforce the outer surface of the throat portion against cracking caused by fatigue due to repeated engagement with the nose portion of a mating knuckle. An example of this knuckle construction can be found in Canadian Pat. No. 540837. Other forms of reinforcement for the throat and inner surface of the cavity were provided by forming an annular collar in the core area at about the midportion between the top and bottom pin hole openings in the knuckle. Sometimes, instead of an annular collar, the core area was eliminated so that the pin extended through an enlarged hole in an otherwise solid knuckle. The dimensional relationship between the parts was such, however, that the knuckle pin was unrestrained against bending transverse to its length within dimensional limits sufficient to prevent fatigue failure of the knuckle pin.